John Le Carré could be forgiven for putting his feet up and having a rest, given that he's spent the past 50 years defining the British spy novel. In fact, the author has been enjoying something of a purple patch with his most recent offerings, moving away from his traditional Cold War setting to tackle all sorts of modern multinational corruption, political subterfuge and criminal activity.

This time around, he is having a timely pop at the behaviour of the international banking community, as well as the Russian mafia and, as is usual, the subtle machinations of the British Secret Service. It's an intriguing and ultimately captivating story, but not without its structural and characterisation problems.

Perry Makepeace is a young, jaded English lecturer at Oxford University; his girlfriend, Gail Perkins, is a beautiful and promising barrister. On a rather uncharacteristic holiday in Antigua, they encounter Dima, a larger-than-life Russian bear of a man who happens to be the major money launderer for the Russian mafia.

The meeting is not accidental on Dima's part, as he is looking to escape a highly threatening situation and willing to whistleblow on the entire organisation in exchange for a new life courtesy of British Intelligence. So Perry and Gail take his message back with them to Britain, where they somewhat implausibly find the appropriate ears to tell it to, thus setting in motion the plot wheels that keep turning towards a genuinely tense ending.

The characters of Perry and Gail are rather too thin to spend all this time with, and Le Carré is on more solid ground with his cast of intelligence officers, from Hector the bluff old maverick to Luke, saved from a career of pen-pushing by this one last operation in the field. Le Carré also does a great job of painting Dima and his entourage, creating one almighty dysfunctional family with a classically likeable rogue at its head.

But Our Kind of Traitor is slow to get going. The first 100 pages consist of Perry and Gail recounting their meeting with Dima to members of the Secret Service, giving the encounter a second-hand distance that lessens its impact. The next third of the book doesn't fare much better: another 100 pages of talking, in which intelligence officers and the unlikely couple work out what they're going to do about Dima's offer to come in and tell all. At least here we also get to see the intricate connections between billions of illegal Russian dollars, the amoral London banking community, and the politicians in the pockets of both, who grease the wheels and ensure that all nests are well-feathered.

The notion that colossal amounts of illegitimate money from black-market sources have kept the banking world afloat in recent years should perhaps not be surprising, but it's still shocking to see it laid bare, and Le Carré is, as ever, adept at convincing the reader without seeming too tub-thumping about it.

The action then swings to Paris and on to Berne, as Dima desperately seeks an escape route before he's assassinated, and with the book ending on a typically downbeat note, Le Carré's disgust at the world he depicts is clear – something which has real impact despite his novel's occasional flaws.